863af1b8a4
This is designed to handle race conditions, where the strand is deleted between when the object is retrieved and when incr_* is called. One caller of Semaphore.incr, SemSnap.incr, relies on the Semaphore being returned. Update this method handle the case where nil is returned by Semaphore.incr. An alternative approach would be raising an exception for this case. That can potentially alert us to cases that pass invalid strand ids, but it would require more code to handle race conditions. We couple have separate methods, one that raised by default, and another than can be used in cases where we know the strand id is correct, but want to avoid a race condition. However, I'm not sure the complexity is worth it. While here, omit unnecessary hash values, switch from create_with_id to create, and explicit dataset call, and unnecessary explicit receiver.
58 lines
1.1 KiB
Ruby
58 lines
1.1 KiB
Ruby
# frozen_string_literal: true
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class SemSnap
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def initialize(strand_id, deferred: false)
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@deferred = deferred
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@strand_id = strand_id
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@extant = Hash.new { |h, k| h[k.intern] = [] }
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@defer_delete = []
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Semaphore.where(strand_id: @strand_id).each do |sem|
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add_semaphore_instance_to_snapshot(sem)
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end
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end
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def self.use(strand_id)
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new(strand_id, deferred: true).use do |snap|
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yield snap
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end
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end
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def use
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yield self
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ensure
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apply
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end
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def set?(name)
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name = name.intern
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@extant.include?(name)
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end
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def decr(name)
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name = name.intern
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ids = @extant.delete(name)
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return unless ids && ids.length > 0
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@defer_delete.concat(ids)
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apply unless @deferred
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end
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def incr(name)
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if (semaphore = Semaphore.incr(@strand_id, name))
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add_semaphore_instance_to_snapshot(semaphore)
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end
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end
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private
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def apply
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return if @defer_delete.empty?
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Semaphore.where(strand_id: @strand_id, id: @defer_delete).destroy
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@defer_delete.clear
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end
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def add_semaphore_instance_to_snapshot(sem)
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@extant[sem.name.intern] << sem.id
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end
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end
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